This invention relates to scaling devices, and is more particularly directed to a scaling device in which a reading head provides signals corresponding to indicia recorded on a scale member to indicate accurately any relative displacement between the head and the scaling member. Such a scaling device finds favorable application, for example, in the control of automatic machine tools or industrial robots.
Scaling devices for the direct measurement of displacement of a work table, machine tool, work piece, or movable elements of a machine, are well known. In these devices, a linear scale, for example, a magnetic scale, can operate substantially as disclosed in U.S. Pat. No. 3,597,749. Alternatively, a photoelectric scale can be used. Other previous-employed scaling devices can operate, for example, as shown in U.S. Pat. No. 2,799,835.
Such scaling devices normally employ a scaling mechanism disposed within a casing, and relative displacement in an associated machine or machine tool is detected by means of a detecting element mounted on a carrier extending through an opening in the casing.
Unfortunately, previously-proposed scaling devices require large openings in the casings thereof to permit displacement of the carrier. Therefore, such devices are difficult to construct to be sufficiently waterproof, oilproof, and dustproof. As a result, such conventional devices cannot be used for extended periods of time under adverse factory conditions where there is a substantial amount of dust, oil, particles of magnetic material, or other contaminants in the atmosphere.